Japanese Patent Laying-Open No. Sho 51-83654 discloses a blood testing container wherein a thixotropic serum or plasma separator composition, such as a mixture of silicone and silica, has been accommodated at the bottom of a blood collection tube. Blood is collected in the blood collection tube, left to stand for an appropriate period of time and centrifuged. Then, the gel-like serum or plasma separator composition is rendered flowable by the action of a centrifugal force. Also, the gel-like serum or plasma separator composition has a specific gravity (1.03–1.07) intermediate between a serum or plasma component (specific gravity of about 1.02) and a blood clot or cell component (specific gravity of about 1.08). Accordingly, the separator composition gradually rises in the collected blood from the bottom of the tube and positions between the serum or plasma layer and the blood clot or cell layer to define a partition which successfully separates the serum or plasma component from the blood clot or cell component. The serum or plasma component now separated from the blood or cell component can be removed easily from the blood collection tube for submission to various testings. It can also be stored without transferring to another container.
Such a thixotropic serum or plasma separator composition may comprise main components other than those described above. For example, separator compositions have been proposed which, besides the aforementioned silicone, also contains an oligomer and an agent for adjustment of specific gravity, viscosity and/or thixotropic properties. Examples of oligomers include halogenated hydrocarbon oligomers (Japanese Patent Laying-Open Nos. Sho 55-43462 and Hei 09-124743), acrylate ester oligomers (Japanese Patent Laying-Open Nos. Sho 53-42283 and Hei 4-337458), ester oligomers (Japanese Patent Laying-Open No. Sho 58-137757 and Japanese Patent Kohyo No. Hei 9-501192), α olefin-maleate ester oligomers (Japanese Patent Laying-Open No. Sho 58-35463) and cyclic hydrocarbon oligomers (Japanese Patent Laying-Open Nos. Hei 02-95257 and Hei 09-15238). Examples of adjustment agents include inorganic particles such as of silica and kaolin and organic gelation agents such as benzylidene sorbitol.
However, the preceding silicone resins show markedly poor compatibility with the specific gravity and viscosity adjusting agents comprised of the inorganic particles and are highly susceptible to phase separation within a short period of time. Also, the silicone resins undergo a curing reaction when they are subjected to radiation (γ-ray, electron beam or the like) sterilization. Accordingly, the silicone reins are currently little used.
The halogenated hydrocarbon oligomers, when incinerated for disposal, produce halogenated hydrogen gas which possibly gives damage to incinerators or exerts a bad influence upon the environment.
The preceding acrylate ester oligomers, ester oligomers and α olefin-maleate ester oligomers each contains many polar groups in a molecule, which problematically increase the occurrence of drug adsorption when a drug concentration in blood is monitored.
The separator composition containing a phthalate ester and a cyclopentadiene resin as the cyclic hydrocarbon oligomer, as disclosed in Japanese Patent Laying-Open No. Hei 09-15238, is excellent in two respects; drug adsorption is maintained at a low degree of occurrence and generation of toxic incineration gas is avoided. However, the composition contains components which are poorly compatible with each other. On rare occasions, a separated oily component is observed to float in blood serum or plasma after centrifugation.